Even with lots of gravel, rocks,etc, a 55g standard has about 580 sq. inch foot print, less than 1 lb. per sq. inch. I am 6'1" tall and weigh about 185lbs, size 11 shoes, that translates to about 2+ lbs per square inch with both feet ont the ground, double if I stand on one foot. If worried about rotten flooring place thew tank stand on a plywood platform, just a 18" x 60" sheet of 1/2" ply. otherwise don't sweat it.